A Rough and Ready Guide To Priming Sugar And Carbonation

Priming is an important part of home brewing. Without it you won’t have much foam or aroma and your brew won’t look at lot like beer.

So here’s a guide to priming sugar including how to use just the right amount.

adding priming sugar to fermenter

The importance of carbonation is sometimes overlooked, but it’s one of the most noticeable sensory aspects of beer.

It affects appearance, smell and mouthfeel and, I suspect, flavour. So it’s important to get it right.

The usual way to carbonate bottled beer is by adding priming sugar.

On the face of it the principles are simple: treat the yeast to a little more sugar while they’re in the bottle and they’ll reward you with gas.

But while there are rules of thumb about how much priming sugar to add – 4 oz (113 g) per 5 gallons (19 litres) or, the old school version, a teaspoon per bottle – I find that the results often vary.

Fed up with the situation I decided to find out more about it, and have prepared this guide explaining what it’s all about.

It may not sound like the most riveting subject for a blog post but there’s no doubt it’s useful stuff when brewing.

(I’m talking about carbonation in bottles with priming sugar. This Brew Strong show contains information on force carbonation in kegs, if you’re interested in that.)

What is Priming Sugar?

As I’ve already mentioned, priming sugar is sugar added to home brew before packaging to give it gas and head.

Although carbon dioxide is produced throughout the main fermentation most of it escapes through the airlock, carrying away unwanted elements as it goes.

So when you bottle the beer, to all intents and purposes it’s flat.

By adding priming sugar as the beer goes into the bottles, you encourage the yeast to generate more carbon dioxide. This time, because the bottles are sealed, it becomes part of the beer.

Most sugars work for priming although some are better than others.

Types of Sugar To Use For Priming Beer

More often than not brewers want to add priming sugar without changing the beer flavours.

Table and corn sugar are popular, flavourless options. But you can use more or less anything.

Sometimes you may want the priming sugar to add extra layers of flavour. I’ve primed with honey, for example, attempting to maximise those flavours in (unsurprisingly) a honey beer.

Similarly, I often use brown sugar in dark ales and bitters because I think those flavours marry well.

Perhaps the impact is negligible, but it feels right when the ingredients are consistent throughout the brew process.

When choosing priming sugar, think of the flavours you want to add. If it’s not important, use white sugar.

Priming Sugar and Amount of Gas

You can describe the amount of gas in a beer with the term “volume”. The unit is the same as the one you use to measure your beer, usually gallons or litres.

1 volume = 1 litre/1 gallon of CO2 in 1 litre/1 gallon of beer

The more priming sugar you add the more gas you get. But how much do you want?

While to some extent it’s a matter of taste, different types of beer traditionally have different amounts of carbonation.

This table is adapted from guidelines in How To Brew, and shows typical volumes of CO2 in different types of beer:

beer carbonation levels chart

Knowing how much gas is needed, you can work out how much priming sugar to use to get it.

Unfortunately, and as ever, it’s not entirely straightforward because when the beer comes out of the fermenter it actually contains some residual CO2.

CO2 After Fermentation and the Effect of Temperature

Carbonation of liquids is governed by Henry’s Law.

It gets complicated quickly (and is beyond my ability or desire to go into it in much detail!), but the key thing is that the amount of gas in the beer depends on the temperature and pressure.

As I understand it, over time the gas dissolved in the liquid will reach equilibrium with it’s surroundings. Inside the fermenter the head space is almost entirely CO2 so in the liquid there’s a good amount of gas.

Liquid is able to take in more gas at lower temperatures, so the warmer the beer the less gas. I wonder if this explains why it’s traditional for lagers to be carbonated higher than ales.

In any case, it’s why most priming sugar calculators ask for bottling temperature.

Priming Sugar Calculations

This Home Brew Digest article is a good primer on carbonation in general, and explains how to calculate the amount of priming sugar needed to achieve a certain amount of gas.

It includes a table of the CO2 already in the beer, according to temperature, which I’ve interpreted here:

beer carbonation levels existing

You can use that information to work out how much gas to add:

={Volumes To Add}={Target Volumes}-{Residual Volumes}

According to the article, it takes 4 grams of table sugar (sucrose) per litre to produce 1 volume of CO2, so:

={Priming Sugar}={Volumes To Add}*{4}*{Volume Of Beer}

To get 2.5 volumes of gas into 20 litres of beer at 14°C, for example:

={Volumes To Add}={2.5}-{1.05}={1.45}

={Priming Sugar}={1.45}*{4}*{20}={116 g}

(These conversion tables go between grams and ounces, gallons and litres).

Although you can calculate manually, it’s most common to use brewing software to work out priming sugar amounts.

I find the Northern Brewer one useful because it includes a wide variety of fermentables.

I cross checked a few sample calculations with the above formulae and they more or less coincide.

As I researched this post I came across this article which elaborates on the idea, making it clearer.

However, in the second article the alleged contribution of sucrose to carbonation is different, 3.5 g per litre instead of 4 g.

As usual the various disagreeing sources mean that to get to the bottom of it it’s best to test on your own set up and adjust according to experience.

I feel a side by side experiment coming on.

Having said that, I’m not especially bothered by approximations as everything in my process is rough and imprecise. If it’s different on your system I don’t believe you!

More than anything, looking at sample calculations can help you understand the principles:

  • More sugar makes more gas
  • Priming at warmer temperatures requires more sugar

Priming Sugar Quick Reference Guide

Using the Northern Brewer calculator I’ve extracted some commonly used priming sugar amounts to save time on brew day.

I’ve calculated for low, medium and high carbonation. I don’t believe I measure temperature accurately enough, or therefore know how much carbonation’s already in the beer, to bother being more precise than that.

Bear in mind that I’m used to British beers and depending on where you’re from, my idea of high carbonation may be different to yours.

beer carbonation chart: low medium high

These amounts of white sugar are needed to prime beer:

Volume of Beer (gallons/litres)Light
(1.75 vols)
Medium
(2.25 vols)
High
(3 vols)
1 gallon0.4 oz0.7 oz1.1 oz
2 gallons0.9 oz1.4 oz2.1 oz
3 gallon1.4 oz2.1 oz3.2 oz
4 gallons1.8 oz2.8 oz4.3 oz
5 gallons2.3 oz3.5 oz5.3 oz
2 litres7 g10 g16 g
4 litres14 g21 g32 g
6 litres20 g31 g48 g
8 litres27 g42 g64 g
10 litres34 g52 g80 g
12 litres41 g63 g96 g
14 litres48 g73 g112 g
16 litres54 g84 g127 g
18 litres61 g94 g144 g
20 litres68 g104 g159 g

As well as the flavour differences, using other sugars also affects how much carbonation you get.

These conversion factors take that into account:

FermentableConversion Factor
Brown Sugar1.13
Corn sugar/Dextrose1.10
Honey1.35
White Sugar1

The amounts in the table are for beer at 21°C /70°F. In very rough terms, add or subtract 2 grams / 0.03 oz ounces per °C/°F to account for temperature differences.

How To Add Priming Sugar

Finally, the important part. Adding priming sugar to your beer.

First make sure fermentation is over. If there are still fermentable sugars in the beer they will, most likely, eventually be used by the yeast.

In this scenario adding priming sugar could potentially cause over carbonation and the risk of exploding bottles. Strong beers are particularly susceptible.

Anyway, on bottling day, heat 450 ml water in a pan and dissolve in the priming sugar before boiling for ten minutes.

Leave to cool and pour into the beer, stirring gently to ensure even distribution.

With a bottling bucket it’s even easier. Just put the solution in the bucket before racking in the beer. It mixes itself as the bucket fills.

The key to consistent carbonation is mixing well so the priming sugar is distributed throughout the batch.

Phew. That’s enough for now.

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Comments...

  1. Wow. This is an incredible helpful, insightful post. Thanks so much for all the legwork on this. Well done.

    • John

      Thanks Bryan, I hope it’s useful.

  2. Colin

    Thanks for the insight. I’m doing an Porter, and want to use brown sugar…any thoughts. I see the conversion factor is 1.13, is that still valid?

    • John

      Yes, that factor should be OK. I’d go between light and medium carbonation in a porter but it’s a matter of personal preference of course.

      There’ll inevitably be some trial and error with your own ingredients and set-up because, apart from anything else, there’s variety in brown sugars.

      These tables are a good starting point – I use them myself – and you can always tweak the next batch if you under or overshoot. Just be careful not to use too much.

      Cheers!

  3. Rex

    I agree. This article (and entire website in fact) is immensely helpful.

    • John

      Thanks! I’m glad the information’s of use.

  4. Phil

    I was looking for some info that would give me a rough and ready guide as to starting and final gravities and more importantly getting the fizz in to the bottle.

    This site and guide gave me everything I needed, not just the raw numbers but also comparison’s with various beers so that I have a real idea of what I should be aiming for, rather than the usual and very subjective Low / Medium / High.

    Thank you for taking the time and trouble to put it all together in a way that is not only useful for the dedicated brewer in search of the holy grail but also informative and easy to understand by the
    “chuck it in a bucket and see what happens” brigade.

    Many Thanks.

    Phil.

    • John

      Thanks for taking the time to comment.

      Happy brewing!

  5. Ruby Duck

    As a born-again kit brewer (used to do it in the 70s and 80s) I’m greatly impressed by the quality of the current kits and am now on my fifth bottling.

    I used ordinary cane sugar for the first (Woodforde’s Nelson’s Revenge) and the result was nectar, but there was a lot of very loose sludge that made pouring difficult. I then did a wilko kit using brewing sugar for priming. While the beer wasn’t a patch on the Woodforde’s (not bad at all, but not so much to my taste), the sludge was nice and firm and stayed put at the bottom of the bottle. The next – a Woodforde’s Wherry – primed with dextrose also had a nice tidy sludge.

    Before I bottle my next batch of Nelson’s, I’d be interested in finding out whether the sludge problem with the first batch was down to possibly bottling a bit early (SG was stable for 12 hrs, but we were going away so didn’t spend a lot of time considering whether to proceed) or had something to do with using cane sugar rather than brewing sugar (dextrose).

    There is also a faintly sweet after-taste to the brews primed with dextrose. Is that the dextrose, or is it more likely to be a feature of the particular kits?

    • John

      Ruby,

      It sounds like the sludge may be yeast that hasn’t settled to the bottom. It could be that you aren’t leaving the beer long enough at each stage.

      I would usually leave the fermentation for two weeks, then at least another two weeks in the bottle and ideally more. How long are you leaving everything?

      The sweet taste, if not a result of the beer’s recipe, is most likely because the fermentation hasn’t finished and there are still too many sugars in the liquid.

      Again, this could be because you haven’t left it long enough, but it could also be that for one reason or another the fermentation has stuck. In that instance you could try pitching another sachet of yeast to see if that dries it out a bit.

      Dextrose shouldn’t be causing the sweetness, because it is completely fermentable.

      Does that help?